Fluorescent two-photon absorption benzothiadiazole dyes having photoreleasing quenchers

Article abstract of DOI:10.1246/cl.2009.1042

Fluorescent two-photon absorption benzothiadiazole dye 5 provides significant fluorescence quenching by introducing nitrobenzene quencher moieties. The florescence intensity is recovered by photoreleasing of the quencher moieties upon irradiation. Copyrig

Full text of DOI:10.1246/cl.2009.1042

1042
Chemistry Letters Vol.38, No.11 (2009)
Fluorescent Two-photon Absorption Benzothiadiazole Dyes
Having Photoreleasing Quenchers
Tsutomu Ishi-i,ꢀ1 Nami Nakamura,1 Tomonori Mine,1 Satoru Imamura,2 Motoyuki Shigeiwa,2
Hideki Gorohmaru,2 and Shuuichi Maeda2
1Department of Biochemistry and Applied Chemistry, Kurume National College of Technology,
1-1-1 Komorino, Kurume 830-8555
2Mitsubishi Chemical Group Science and Technology Research Center, Inc.,
1000 Kamoshida-cho, Aoba-ku, Yokohama 227-8502
(Received August 21, 2009; CL-090771; E-mail: ishi-i@kurume-nct.ac.jp)
Fluorescent two-photon absorption benzothiadiazole dye 5
provides significant fluorescence quenching by introducing nitro-
benzene quencher moieties. The florescence intensity is recov-
ered by photoreleasing of the quencher moieties upon irradiation.
Pd(PPh3)4
O
O
Br
Br
+
NHBoc
B
Na2CO3 aq/DME
Y. 74%
N
N
2
S
1
CF3COOH
BocNH
NHBoc
H2N
NH2
CH2Cl2
N
N
N
Two-photon absorption (TPA) dyes with photoresponse
have been of much interest in recent years in view of their poten-
tial application for three-dimensional (3D) optical data storage.1
The two-photon excitation has a quadratic dependence on the in-
put laser intensity, leading to a pinpoint excitation at the point of
a focused laser beam.2 Thus, two-photon-based data storage sys-
tems have an advantage of high spatial resolution in multiple da-
ta storage layers to achieve high density memory. In 3D optical
data storage, photoresponsive materials with TPA activity have
been used such as photochromic compounds,3 photopolymeriza-
tion initiators,4 and fluorescence turn-on and turn-off dyes,5 in
which TPA activity as well as high photoresponse are required
at the same time.
N
S
3
S
Y. 87%
4
NO2
HN
NO2
NH
Cl
O2N
N
N
K2CO3/DMF
Y. 40%
S
5
Scheme 1. Preparation of 5.
DMF/POCl3
N
N
CHCl2CHCl2
N
N
Here, we propose a new concept in 3D optical data storage,
in which fluorescent TPA dye and photoreleasing fluorescent
quencher are combined. The principle idea in the study is fluo-
rescent quenching of TPA dye by introducing a quencher, and
the subsequent fluorescence recovery by photoreleasing of the
quencher moiety upon two-photon irradiation to store the data.
Data reading is achieved by monitoring the fluorescence intensi-
ty change. Amino-substituted benzothiadiazole (BTD) dye is a
potential candidate as a parent of storage media because of its
high TPA activity as well as strong fluorescence.6 In contrast,
2-nitrobenzyl functional group is selected as the photoreleasing
quencher, because the function has been used as a photolabile
protecting group in caged compounds,7 and the nitrobenzene
moiety has been well known as a strong fluorescence quencher
via photoelectron transfer (PET).8 In this letter, we report that
amino-substituted BTD dyes having two nitrobenzyl functions
provide significant fluorescence intensity change from weak to
strong emission by photoreleasing of the nitrobenzyl functions.
Aminophenyl-subsituted BTD derivative with two nitroben-
zyl functions 5 was obtained from 4,7-dibromo-2,1,3-benzothia-
diazole (1)9 in three steps (Scheme 1). Suzuki coupling of 1 with
boronate 2 in the presence of a palladium(0) catalyst provided 3
with Boc-protected aminophenyl groups. Deprotection was car-
ried out by treatment with trifluoroacetic acid to give 4. Finally,
the two nitrobenzyl functions in 5 were introduced by the reac-
tion of 4 with 2-nitrobenzyl chloride.
Y. 84%
S
6
OHC
CHO
HCl/H2N
O2N
NaBH4
N
N
Et3N
N
N
Y. 13%
MeOH/THF
S
7
HN
NH
NO2
NO2
N
N
N
N
S
8
Scheme 2. Preparation of 8.
amino)phenyl]-2,1,3-benzothiadiazole (6)6 in two steps
(Scheme 2). Compound 6 was transformed to the corresponding
diformyl derivative 7 by the Vilsmeier reaction. Finally 8 was af-
forded from the condensation reaction of 7 with 2-nitrobenzyl-
amine followed by treatment with sodium borohydride. Identifi-
cation of 3, 4, 5, 7, and 8 was performed by means of spectro-
scopic methods and elemental analysis.
In toluene and dichloromethane, 4 shows an absorption band
around 440 nm, which is assigned to the transition from the
electron-donating amino moiety to the electron-accepting BTD
Triphenylamine-subsituted BTD derivative bearing two ni-
trobenzyl functions 8 was obtained from 4,7-bis[4-(diphenyl-
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.11 (2009)
1043
(a)0.3
(b)
H2N
NH2
+
h
ν
NO
ON
4
5
5
+
N
N
0.2
CHO
S
OHC
4
ε
4
5
0.1
Scheme 3. Photo-releasing reaction of 5.
(Figure 1c), indicating that the desired photoreleasing of the ni-
trobenzyl functions really occurs to provide fluorescent 4
(Scheme 3).7
0
250
350
450
550
500
550
600
650
700
750
Wavelength/nm
Wavelength/nm
In conclusion, we have demonstrated that fluorescent emis-
sion from two-photon absorption benzothiadiazole dye is
quenched by introducing nitrobenzyl functional groups. The
quencher moieties are released by light irradiation to recover
the emission intensity. We believe that the present system will
be developed to three-dimensional data storage systems using
two-photon excitation.
(c)
after
before
References and Notes
1
2
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450 500 550 600 650 700 750
Wavelength/nm
Figure 1. (a) UV–vis and (b) fluorescence spectra of 4 and 5 in
dichloromethane at 1 ꢁ 10ꢂ5 and 1 ꢁ 10ꢂ6 M, respectively. (c)
Fluorescence spectra of the PMMA film sample including 5
(1 wt %) before and after UV-light irradiation (325 nm).
3
moiety (Figure 1).6,10 In 5, the absorption band was scarcely
changed by introducing nitrobenzyl functions, indicating that
any electronic interactions between the BTD and nitrobenzene
chromophores do not occur in the ground state. Similar spectral
properties were found in 6 and 8, which show an absorption band
around 460 nm.10
The single-photon absorption around 440–460 nm in 4, 5, 6,
and 8 is very suitable for two-photon excitation at 800 nm by
using a femtosecond Ti:sapphire laser source. Thus, TPA
cross-sections (ꢀ) were measured by using an open aperture Z-
scan method with the femtosecond laser pulses, as reported in
our previous work.6 At 800 nm, 4, 5, 6, and 8 display ꢀ values
of 12, 20, 84,6 and 111 GM, respectively, which are comparable
to the values of BTD dyes reported previously.6
4
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¨
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A significant effect of the introduced nitrobenzene quencher
moieties was observed in the fluorescence spectra. In dichloro-
methane, a red emission at 628 nm observed in 4 without nitro-
benzene moieties was quenched significantly in 5 with nitroben-
5
6
a) H. E. Pudavar, M. P. Joshi, P. N. Prasad, B. A. Reinhardt,
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zyl functions (Figure 1b). The florescence quantum yield (ꢁFL
)
changed from 0.25 (4) to 0.009 (5), indicating that the desired
PET really occurs from the BTD florescent chromophore to
the nitrobenzene quenchers. The PET efficiency decreased in
nonpolar toluene solution: ꢁFL changed from 0.59 (4) to 0.44
(5). In triphenylamine-substituted BTD system, very weak fluo-
rescence quenching occurred: ꢁFL ¼ 0:62 (6) and 0.54 (8) in tol-
uene, and 0.36 (6) and 0.30 (8) in dichloromethane.10
Photoreleasing of the nitrobenzyl functions was performed
in the BTD dye-doped polymer matrix medium. A PMMA film
including 5 (1 wt %) was prepared by spin coating from toluene
solution. Upon UV-light irradiation at 325 nm, the emission
intensity around 600 nm is enhanced by a factor of 5 times
7
8
9
Y. V. Il’ichev, M. A. Schworer, J. Wirz, J. Am. Chem. Soc.
¨
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10 Supporting Information is available electronically on the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/
index.html.
Published on the web (Advance View) October 3, 2009; doi:10.1246/cl.2009.1042